Despite recent advances
in bioinspired underwater adhesives, achieving
tough, fast, and stable adhesion in aqueous environments is still
challenging. Here, an underwater super-tape with semi-interpenetrating
polymer networks (SIPNs) and a water-repelling liquid surface is synthesized.
In the SIPN, the linear chains easily diffuse to adapt to the adherends,
and the cross-linked chains provide the super-tape with high dimensional
stability. Meanwhile, both the linear and cross-linked chains bear
many catechol groups, which can not only vigorously interact with
the adherends but also form numerous hydrogen bonds serving as sacrificial
bonds in the SIPN. Thus, the super-tape shows both high interfacial
adhesion and cohesive energy. Moreover, the super-tape is covered
with a water-repelling liquid surface by spraying it with traces of
a hydrophobic solvent. It is demonstrated that the hydrophobic solvent
absorbed on the surface of the super-tape can remove water between
the tape and adherends, enabling their intimate contact to form a
strong interaction. As such, the super-tape shows excellent instant
adhesion property under water, and the adhesive strength and toughness
increase with time and reach their maximum values at around 5 h. The
maximum debonding energy of the super-tape reaches 3933 J m–2, which is much higher than those of existing double-sided tapes.
Four types of self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular beam epitaxy and studied via temperature-dependent and time-resolved photoluminescence (PL) spectroscopy measurements. A thin InGaAs stain reducing layer (SRL) is adopted which extends the emission wavelength to 1.3 μm and the influence of strain on QDs is investigated. The SRL releases the strain between the wetting layer and QDs, and enlarges the size of QDs, as shown by atomic force microscopy measurements. As the thickness of InAs layer decreases to 1.7 ML, the QDs with the SRL are chained to strings and the density of QDs increases significantly, which leads to an abnormal redshift of 1.3 μm PL peak at room temperature. PL peaks of InAs QDs with the SRL show redshift compared with the QDs directly deposited on GaAs matrix. The dependences of PL lifetime on the QD size, density and temperature (T) are systematically studied. It is observed that the PL lifetime of QDs is insensitive to T below 50 K. Beyond 50 K, increases and then drops at higher temperature, with a peak at TC, which was determined by the SRL and the thickness of InAs. We have also observed an obvious PL spectral redshift of the QDs with 1.7 ML InAs coverage on SRL at low T as the measuring time delays. The PL lifetime of QDs with the SRL is smaller than that of QDs without the SRL. The QDs with different densities have different PL lifetime dependence on the QDs size. These observations can be explained by the competition between the carrier redistribution and thermal emission.
Three different InAs quantum dots ͑QDs͒ in an InGaAs/ GaAs quantum well were formed and investigated by time-resolved and temperature dependent photoluminescence ͑PL͒. A strong PL signal emitting at ϳ1.3 m can be obtained at room temperature with a full width at half maximum of only 28 meV. Dots-in-a-well structures result in strong stress release and large size InAs QDs which lead to narrowing and redshifting of PL emissions, enhancement of carrier migration, increasing carrier density in QDs, achievement of good PL lifetime stability on temperature, and improving the QD quality.
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